Process for treating metal articles

ABSTRACT

Metal articles are coated by a process which comprises treating the metal articles with a non-aqueous phosphatizing solution containing a novolac phenol-formaldehyde resin having a molecular weight of from about 300 to 5,000, and chemically reacting the resin by heating the treated article at a temperature of at least about 190*C in the presence of an oxygen-containing atmosphere. The articles so treated are rendered exceptionally corrosion resistant and exhibit excellent retention of final finish coatings.

United States Patent 1191 Shatz et al.

1451 Feb. 25, 1975 1 PROCESS FOR TREATING METAL ARTICLES [73] Assignee:Hooker Chemical Corporation,

Niagara Falls, NY.

[22] Filed: Jan. 12, 1973 [21] Appl. No.: 323,176

52 us. c1. 148/615 R, 117/132 BF [51] Int. Cl. C231 7/08 [58] Field ofSearch 148/615 R, 6.15 Z; 260/47 P; 117/132 BF [56] References CitedUNITED STATES PATENTS 2,296,070 9/1942 Thompson et a1. 117/69 2,668,1582/1954 Sturm 148/615 R 2,699,413 1/1955 Seagren et al. 148/615 R X2,894,931 7/1959 Somerville et al. 117/132 BF X 2,979,484 4/1961 Redfarn260/47 P X 3,123,582 3/1964 Tryzna 117/132 BF X 3,210,219 10/1965 IJenkins...... 148/615 R 3,409,571 11/1968 Shepard et al. 260/47 P X3,749,611 7/1973 Leon et al. 148/6.15 R

Primary ExaminerMayer Weinblatt Assistant Examiner-John D. SmithAttorney, Agent, or FirmPeter F. Casella; Donald C. Studley; John M.Petruncio [57] ABSTRACT Metal articles are coated by a process whichcomprises treating the metal articles with a non-aqueous phosphatizingsolution containing a novolac phenolformaldehyde resin having amolecular weight of from about 300 to 5,000, and chemically reacting theresin by heating the treated article at a temperature of at least about190C in the presence of an oxygencontaining atmosphere.

The articles so treated are rendered exceptionally corrosion resistantand exhibit excellent retention of final finish coatings.

8 Claims, No Drawings PROCESS FOR TREATING METAL ARTICLES This inventionrelates to the chemical treatment of metal articles. Most particularly,this invention relates to the chemical treatment of metal articles torender the articles exceptionally corrosion-resistant, bettersuited toretain final finish coatings, and resistant to undercutting when finalfinish coatings are so applied.

It is well-known that bonding coatings are desirable on metal articlesto protect such articles from corrosion and to form a base to promoteadherence to such surfaces of organic finishes such as paints, enamels,lacquers, siccative coatings and the like. A variety of processes havebeen developed for this purpose and many specifically differentcompositions have been proposed as satisfactory for use in suchprocesses.

Presently, the majority of bonding coatings techniques entail the use ofphosphate solutions, or phosphatizing solutions. Such phosphatizingsolutions as have been used for the purpose of inhibiting the corrosionof surfaces such as iron and steel result in phosphate coatings which,however, do not provide sufficient protection against corrosion in manycases. In order to obtain sufficient protection against corrosion, thephosphatizing process has been followed in the past, in most instancesby rinsing with dilute chromate solutions.

However, this chromate after-rinsing or aftertreatment of the phosphatecoating has given rise to, among other things, serious disposal problemsrelative to the resulting waste water. Because of the toxicity of thehexavalent and trivalent chromium, these materials must be removedalmost quantitatively from the waste water prior to disposal. Suchrecovery processes as must be practiced render the chromate rinseeconomically less desirable. Further, the chromic acid concentrates usedfor preparing and replenishing the rinsing bath present additionaldifficulties in handling due to their strongly corrosive properties. Theuse of chromate rinses in some instances also gives rise to otherpractical difficulties. During some applications, excessive amounts maytend to either discolor or bleed through subsequently applied topcoats.ln other applications, the solutions may also tend to run or to pool inconfined areas of the metal article to be treated, which may causesubsequent loss of topcoat adhesion when the completed article issubjected to high humidity conditions. Because of the running and/orpooling of the chromate rinsing solution, certain areas of the metalarticles may be inherently left deficient in rinse treatment. Such areasexhibit as a result poor corrosion-resistance and poor resistance toundercutting when exposed to corrosive atmospheres.

Attempts to eliminate or to modify the sealing chromium rinse bypost-treating the phosphatized metal articles with solutions of suchcoating materials as alkene phosphinic acids, acrylics, epoxies and thelike have not resulted in the production of entirely satisfactorycorrosion-resistant metal articles, generally, having anti-corrosive andpaint retention properties attributed to chromium-rinsed phosphatizedmetal substrates.

It is an object of the present invention to provide for protectivecoatings for corrodible metal articles.

It is a further object of the present invention to provide protectivecoatings for corrodible metal articles, which coatings are receptive andretentive to final fini 9 2 t1 It is yet another object of the presentinvention to provide a chemically reactive metal-treating compositionwhich will, when applied to corrodible metal articles, render such metalarticles exceptionally corrosion-resistant.

These and other objects will become readily apparent in view of thefollowing description of the present in- Y t 9&

According to the present invention, an anti-corrosive andpaint-retentive film is formed on the surface of metal articles by theprocess comprising:

a. treating the metal article with a non-aqueous phosphatizing solutioncontaining a novolac phenolformaldehyde resin having a molecular weightof from about 300 to about 5,000; and

b. heating the treated article at a temperature of .at

least about 190C in the presence of an oxygen- The use of phenolicresins to prevent corrosion and It has now been found that verylowinolecular weight novolac phenol-formaldehyde resins applied to metalarticles simultaneously with the application of a conventionalphosphatizing treatment the resin being deposited in the amounts of fromabout 4 to about 400 milligrams per square foot, and the treated metalarticle subsequently heated at temperatures in excess of about C in thepresence of an oxygen-containing atmosphere, provide for remarkablysuperior corrosion protection and other performance properties. Further,such resin depositions do not behave as barrier layers, as do the highmolecular weight phenolic resins currently used in the art. Apparently,when the phosphate and low molecular novolac containing compositions areheated to temperatures inexcess of about C in the presence of anoxygen-containing atmosphere, the resins tend to exhibit chemical,rather than contiguous film-forming behavior. It is believed that, attemperatures in excess of about 190C, and in presence of oxygen, the lowmolecular weight novolac phenolformaldehyde resins complex and reactwith the phosphate crystals and iron oxides present to formcausticinsoluble complexes, and that it is this causticinsolubility ofthe formed complexes which provides for the excellent undercutting andcorrosion resistance properties.

The novolac phenol-formaldehyde resins which have been employed withsuccess in the process of the present invention are those resins havingthe formula: V I

on H

II H2 wherein a is an integer having a value on the order of from about1 to about 50 and b is an integer having a value of from about 1 toabout 20. Such phenolformaldehyde resins as are represented by formula(I), designated as ortho-novolac phenol-formaldehyde resins, aresubstantially phenol-terminated chain polymers in which the phenolicnuclei are united by methylene bridges, for the most part located orthoto the phenolic hydroxyl groups. Those resins as are presented byformula (11), designated as random novolacs, are substantiallyphenol-terminated chain polymers in which the phenolic nuclei are unitedby methylene bridges for the most part located ortho and para to thephenolic hydroxyl groups.

Such resins are further characterized as permanently soluble andthermoplastic, and curable to insoluble, infusible products upon theapplication of heat, or upon the addition thereto of a source offormaldehyde.

The resins are of adequate hardness, with a softening temperature offrom about 50 to a 100C, to permit grinding thereof, exhibit good curingproperties including a fast rate of cure, and attain a high degree ofstrength upon being cured.

Such novolac phenol-formaldehyde resins finding utility in the presentprocess can be prepared by any one of a number of suitable methods knownin the art, such as those disclosed in US. Pat. Nos. 2,475,587 and3,108,978; in Modern-Plastics No. 6,136,220 (1953); and Journal ofPolymer Science 22,477 (1956), the teachings of which are hereinincorporated by reference. The preparation of a typical acid-catalyzednovolac resin is as follows.

A reaction vessel is charged with 1 mol of phenol per 0.8 mol formalin.Approximately 0.2 to 0.3 percent by weight sulfuric acid, based on theweight of phenol, is added following dilution to about 1 N with water.Following the exothermic reaction on the addition of the catalyst, thereaction mixture is heated at reflux for about 2 hours. The reactionmixture is then neutralized with a lime-in-water slurry, dehydratedunder reduced pressure, and discharged from the reaction vessel atelevated temperatures. Following a period of cooling, the resin isrecovered and ground to the proper particle size.

Preparation of the novolac-containing phosphatizing solution isconveniently effected by dissolving a suitable amount of the resin incommercially available nonaqueous phosphatizing solutions. Generally, ithas been found that non-aqueous phosphatizing solutions containing fromabout 3 to about 10 percent by weight of novolac resin are particularlysuited for use in the present process.

The non-aqueous phosphatizing solutions to which the novolac resins areadded generally contain a chlorinated hydrocarbon solvent, phosphoricacid, and a solubilizing agent for the phosphoric acid. Additionally,the phosphatizing composition may contain materials which are effectivein inhibiting or controlling the amount of the phosphate coatingproduced, so as to obtain a hard, thin, substantially uniform phosphatecoating, and materials which are effective in stabilizing the solutionagainst oxidation and thermal degradation.

More specifically, any chlorinated hydrocarbon normally used as adegreasing solvent may be employed in the phosphatizing compositionsused the in present process. Examples of such chlorinated hydrocarbonsinclude trichloroethylene, pe rchloroethylene, tetrachloroethanes,methylene chloride, ethylene dichloride, ethylidene chloride,dichloro-tetra-fluoroethanes, trichlorotrifluoroethanes,trichlorodifluoroethanes, tetraehlorofluorethanes,fluorotrichloroethanes, fluorotetrachloroethanes, methyltrichloroethylene, 1,2- dichloropropane, carbon tetrachloride andmixtures thereof. The chlorinated hydrocarbons used may be unstabilizedor, if desired, may contain one or more of the various known stabilizerswhich are effective in pre venting or inhibiting the decomposition ofthe chlorinated hydrocarbon.

Of the chlorinated hydrocarbons hereinabove enumerated, the preferredchlorinated hydrocarbon is trichloroethylene.

In addition to chlorinated hydrocarbon solvents such as thosehereinbefore set forth, such organic solvents as aliphatic ketones maybe used in formulating the phosphatizing compositions to which thenovolac resin is to be added. Exemplary of the ketones which may be usedare acetone, methyl ethyl ketone, and the like. Preferably, the primarysolvent used in the present process is trichloroethylene.

The phosphoric acid of the phosphatizing composition is preferably highstrength phosphoric acid. The weight concentration of the phosphoricacid in the phosphatizing composition can be between about 0.1 and about2.0 percent, and preferably between about 0.2 and about 1.5 percent byweight of the phosphatizing solution.

Co-solvents are generally used in such compositions to aid insolubilizing the phosphoric acid. Suitable cosolvents include the 3aliphatic alicyclic alcoholsfExemplary of suitable alcohols are thosealcohols containing between one and about eighteen carbon atoms such asmethyl alcohol; secondary butyl alcohol; amyl alcohol; cyclohexylalcohol; octyl alcohol; decyl alcohol; steary alcohol; mixtures of suchalcohols, and the like. Also suitable for such use are organic compoundsas 2-choroethanol, alkyl acetates such as ethyl acetate, amyl acetateand the like, amides such as N,N-dimethyl formamide and dimethylacetamide, dioxane, monoethers of polyalkylene oxide glycols, anddialkyl sulfoxides. Generally, the co-solvent will be present in thecomposition in amounts within the range of about 1 to about 25 percentby weight of the total composition.

In addition to the above, the phosphatizing compositions may alsocontain various materials which act as stabilizers. Exemplary of suchmaterials are resorcinol, hydroquinone, pyrocatechol, mono-, di andtrialkylated pyrocatechols, alkylated resorcinols, alkylatedhydroquinones, alkylated thioureas, diisobutylene, alkyl phenols,pentaphen, calcium hydroxide and the like.

Generally, the stabilizers are employed in the compositions in amountsof less than about 5 percent by weight. For example, a suitablestabilized composition is one which contains about 0.01 percent byweight 4 tertiary butylpyrocatechol, and 0.4 percent by weightdiisobutylene.

The non-aqueous novolac resin-containing treating solution, as stated,is generally formulated in such manner as to provide a solutioncontaining from about 3 to about percent by weight of the novolac resin.Preferably, those solutions containing from about 3 to about 7 percentby weight of novolac resin are employed. However, the use of more highlyconcentrated or dilute solutions is not thereby precluded.

The novolac resin-containing phosphatizing solution may be applied tothe metal article to be treated by spraying or by dipping the article into the solution to deposit resin in an amount of from about 4 to about400 milligrams per square foot of surface area. The deposition processis usually effected within a period of from about to about 90 seconds ata temperature of about 80C, when using trichloroethylene as the solvent.After the article is sufficiently treated with the resin-containingphosphatizing solution, the article is removed from the treatingsolution and the solvent removed by any suitable means.

Following the removal of the solvent, the treated articlc is then heatedat a temperature in excess of about l90C, generally from about 190 toabout 270C, and preferably at about 205C, in the presence of anoxygen-containing atmosphere for a period of from about 15 seconds to 5minutes, ifdesired. The time required to complete the heat treatment is,of course, dependent upon the make of the resin-containing phosphatizingsolution, the temperature employed and the nature of the article beingtreated. Generally, at a temperature of about 270C, a finished treatmentis provided in less than about 60 seconds.

The treated metal article is corrosion-resistant, exceptionallyreceptive to the application of paints, varnishes, lacquers and otherfinal finish coating compositions. Thus, metal articles treatedaccording to the process of the present invention may receive organicfinishes having as end uses such as automobile finishes, exterior trim,appliance coatings, metal furniture, coatings for venetian blinds,coatings for interior lighting fixtures and the'like.

Metal surfaces which may be treated according to the process of thepresent invention include ferrous metals,

aluminum, galvanized metals, alloys and the like.

Prior to application of the novel treating compositions of the presentinvention, as in accepted phosphatizing practice, thesurface of themetal article to be treated is usually cleansed by physical and/orchemical means such as immersion in or spraying with an aqueous causticcleanser, mechanical abrading or polishing, vapor degreasing or thelike. For the purpose of the present invention it is preferred tocleanse the metal article to be treated by immersing the article for aperiod of about 60 seconds in a commercial aqueous caustic metalcleanser at a temperature of from about 30 to about C. Following thecleansing of the metal article, the article is generally rinsed with hotwater to prevent contamination of the resin-containing phosphatizingsolution, and dried. it is understood that, where a cleansing step isutilized, any suitable cleansing method known in the art may beemployed.

The application of the non-aqueous novolac resincontaining phosphatizingsolution to the metal article to be treated may be accomplished by anysuitable means. Because the solutions are generally applied at atemperature on the order of from about 75 to about C, immersiontechniques are well-adapted for providing the treating materials to themetal article to be treated, The manner of immersion, however, is notimportant in that quiescent baths can be used or, alternately,continuous baths may be advantageously employed.

The temperature of the novolac resin-containing conversion treatingcomposition is preferably maintained at a temperature of from about 75to about 125C during application to the metal article, and the treatedmetal article is subsequently heated at a temperature of from about 190to about 270C for a period of from about 15 to about 180 seconds in thepresence of an oxygen-containing atmosphere.

The following examples serve to illustrate the present invention but arenot to be construed as limiting it hereto.

In the following examples, following the novolac resin-phosphatizingsolution treatment of the metal articles, each metal article was paintedwith enamel and then subjected to 5 percent salt spray and physicaltests. The salt spray test is the American Society for Testing andMaterials (ASTM) test Bl 17-61 with painted panel scribed as given inASTM test D-l6546 1. This test employs a five percent sodium chloridefog or spray. The ratings given depend on the creepage from the scratch,given in one-sixteenths of an inch. Ratings given at spt (S) indicate nocreepage except in a small area. In the salt spray test, unlessotherwise indicated, the exposure time was 120 hours. In the physicaltest, adhesion was determined by knife blade and results are reported onthe scale of 0 to 10, where 10 is excellent, 8 is good, 6 is fair, 4 ispoor, 2 is very poor and 0 is complete loss of adhesion.

EXAMPLE 1 A polished steel panel is cleansed for 60 seconds in acommercial aqueous hot caustic metal cleanser,

rinsed with hot water and flashed in an air circulating oven at 160C.The dried panel is then immersed for 30 seconds in the followingconversion treating composition 87C, following which the panel is heatedat 270C for a period of 90 seconds in an air circulating oven.

Orthonovolac resin (MW I000) wgt. 7r Phosphoric acid 1 Stabilizers 0.42Trichloroethylene 93.58

A conversion coating-type deposition containing less than 1 milligramsof resin per square foot of surface area is formed on the panel. Thetreated panel, when topcoated with commercial melamine alkyd enamel,exhibits a knife blade adhesion rating of 9, an undercutting ofone-sixteenth of an inch and a paint retention of 93 percent.

EXAMPLE 2 The procedure of Example 1 is observed with the exception thatthe treated panel is heated for 120 seconds. The treated panel, whentopcoated, exhibits an undercutting of less than one-sixteenth inch anda paint retention of 96 percent.

EXAMPLE 3 The procedure of Example I is observed with the exception thatthe panel is immersed in the resincontaining phosphatizing solution fora period of 60 seconds. Similar results obtain as in Example 1.

EXAMPLE 4 The procedure of Example 1 is observed with the exception thatthe panel is immersed for 60 seconds and heat-treated for 120 seconds.The treated panel, when topcoated, exhibits a knife blade adhesionrating of 9, an undercutting of less than one-sixteenth inch and a paintretention of 95 percent.

.EXAMPLE 5 The procedure of Example 1 is observed with the exceptionthat the panel is immersed in the resin containing phosphatizingsolution for 90 seconds. Similar excellent results are obtained as inExample 1.

EXAMPLE 6 EXAMPLE 7 The procedure of Example 1 is observed with theexception that the resin-containing phosphatizing solution contains 0.2percent by weight calcium hydroxide, based on the resin content of thesolution. The panel is immersed for a period of 30 seconds andheat-treated for 120 seconds. Similar excellent results obtain as inExample I.

EXAMPLE 8 The procedure of Example 7 is observed with the exception thatthe immersion time is 60 seconds. Similar excellent results obtain as inExample I.

EXAMPLE 9 The procedure of Example 1 is observed with the exception thatthe resin content is 3 percent by weight and the heat-treatment iscontinued for 120 seconds.

' Similar excellent results obtain as in Example I.

EXAMPLE 10 The procedure of Example 9 is observed with the exceptionthat the immersion time is 120 seconds. Similar excellent results obtainas in Example 1.

EXAMPLE 1 1 The procedure of Example 9 is observed with the'exceptionthat the immersion time is 90 seconds and the heating is effected for 60seconds. Similar excellent results obtain as in Example 1.

EXAMPLES 12-13 The procedure of Example 11 is observed with theexception that the heating time is 90 and 120 seconds. Similar excellentresults obtain as in Example 1.

EXAMPLES 14-17 The procedure of Example 11 is observed with theexception that the immersion time is l20 seconds and the heating timesare 30, 60, 90 and 120 seconds. Similar excellent results obtain as inExample l.

EXAMPLES l8-25 The procedure of Example 1 is observed with the exceptionthat the resin content is 7 percent by weight, the immersion times are30, 60, 90, and 120 seconds. Similar excellent results obtain as inExample 1.

EXAMPLE 26 A polished steel panel is cleansed for 60 seconds in acommercial aqueous hot caustic cleanser, rinsed with hot water andflashed in an air circulating oven at 160C. The dry, clean panel is thenimmersed in the following conversion coating composition at 87C, removedand heated at 205C for 150 seconds in an air circulating oven.

Random novolac resin (MW 1000) wgt. 5 Phosphoric acid I Stabilizers 0.42Trichloroethylene 93.5.3 100.00

A conversion coating-type deposition containing less than aboutmilligrams of resin per square foot of surface area is formed on thepanel. The panel when topcoated with commercial melamine alkyd enamel,exhibits properties similar to those of Example 1.

EXAMPLE 27 The procedure of Example 1 is observed with the exceptionthat acetone is employed as the solvent in the phosphatizing solution.Similar excellent results obtain as in Example 1.

EXAMPLE 28 The procedure of Example 26 is observed with the exceptionthat acetone is employed as the solvent in the phosphatizing solution.Similar excellent results obtain as in Example 1.

EXAMPLE 29 The procedure of Example 26 is observed with the exceptionthat acetone/carbon tetrachloride 50:50 is employed as the solvent inthe phosphatizing solution. Similar excellent results obtain as inExample 1.

Similar results as are exhibited in Examples 1-29 are obtained when themolecular weight of'the resin is varied from about 300 to up to about5000 and the heating step is varied from 190C to 270C.

What is claimed is:

l. A process for treating surfaces of zinc, aluminum, ferrous metal andalloys of these to render them corrosion-resistant, paint-receptive andpaint-retentive which comprises a. applying to said surface anon-aqueous phosphatizing composition which consists essentially of 0.1to 2.0 percent by weight phosphoric acid, 3 to percent by weight of anovolac phenol-formaldehyde resin having a molecular weight of fromabout 300 to 5000 and a non-aqueous solvent for said phosphoric acid andsaid resin, said phosphatizing composition being applied in an amountsufficient to provide on said surface a resin coating weight of fromabout 4 to 400 milligrams per square foot and b. thereafter, heating thethus-treated surface at a temperature of at least about 190C in thepresence of an oxygen-containing atmosphere for a period of from about15 seconds to 5 minutes.

2. A process as defined by claim 1 wherein the novolac resin is anortho-novolac resin.

3. A process as defined by claim 2 wherein the resin has a molecularweight of about 1000.

4. A process as defined by claim 1 wherein the novolac resin is a randomnovolac resin.

5. A process as defined by claim 4 wherein the resin has a molecularweight of about 1000.

6. A process as defined by claim 1 wherein trichloroethylene is employedas the solvent in the non-aqueous phosphatizing solution.

7. A process a defined by claim 1 wherein a :50 carbontetrachloridezacetone solution is employed as the solvent in thenon-aqueous phosphatizing solution.

8. A process as defined by claim 1 wherein the surface is treated withthe non-aqueous phosphatizing solution for a period of at least 60seconds and heated at a temperature of about 205C for a period of atleast

1. A PROCESS FOR TREATING SURFACES OF ZINC, ALUMINUM, FERROUS METAL ANDALLOYS OF THESE TO RENDER THEM CORROSION-RESISTANT, PAINT-RECEPTIVE ANDPAINT-RETENTIVE WHICH COMPRISES A. APPLYING TO SAID SURFACE ANON-AQUEOUS PHOSPHATIZING COMPOSITION WHICH CONSISTS ESSENTIALLY OF 0.1TO 2.0 PERCENT BY WEIGHT PHOSPHORIC ACID, 3 TO 10 PERCENT BY WEIGHT OF ANOVOLAC PHENOL-FORMALDEHYDE RESIN HAVING A MOLECULAR WEIGHT OF FROMABOUT 300 TO 5000 AND A NON-AQUEOUS SOLVENT FOR SAID PHOSPHORIC ACID ANDSAID RESIN, SAID PHOSPHATIZING COMPOSITION BEING APPLIED IN AN AMOUNTSUFFICIENT TO PROVIDE ON SAID SURFACE A RESIN COATING WEIGHT OF FROMABOUT 4 TO 400 MILLIGRAM PER SQUARE FOOT AND B. THEREAFTER, HEATING THETHUS-TREATED SURFACE AT A TEMPERATURE OF AT LEAST ABOUT 190*C. IN THEPRESENCE OF AN OXYGENCONTAINING ATMOSPHERE FOR A PERIOD OF FROM ABOUT 15SEONDS TO 5 MINUTES.
 2. A process as defined by claim 1 wherein thenovolac resin is an ortho-novolac resin.
 3. A process as defined byclaim 2 wherein the resin has a molecular weight of about
 1000. 4. Aprocess as defined by claim 1 wherein the novolac resin is a randomnovolac resin.
 5. A process as defined by claim 4 wherein the resin hasa molecular weight of about
 1000. 6. A process as defined by claim 1wherein trichloroethylene is employed as the solvent in the non-aqueousphosphatizing solution.
 7. A process a defined by claim 1 wherein a50:50 carbon tetrachloride:acetone solution is employed as the solventin the non-aqueous phosphatizing solution.
 8. A process as defined byclaim 1 wherein the surface is treated with the non-aqueousphosphatizing solution for a period of at least 60 seconds and heated ata temperature of About 205*C for a period of at least 60 seconds.